1. Field of the Invention
This invention generally relates to improving the reception of a broadcast, cable or game port television signal, and more particularly relates to isolating alternate paths of the television signal.
2. Description of the Prior Art
As towns and cities become more populated, the number of obstructions to broadcast signals, such as those used for television and radio, also increases. These obstructions introduce substantial signal reflections, which result in intolerable reductions in the signal-to-noise ratio (SNR) of the broadcast signal after it is received. Additional factors that decrease the SNR include the increased use of cellular and mobile communications, broadcast signals that are received over greater distances, and the increased utilization of available bandwidth.
Amplification of the broadcast signal can largely overcome problems associated with reductions in the SNR. However, amplification is neither always necessary nor desirable, such as when a receiver is in close proximity to a transmission station. In this case, providing an alternate path for the broadcast signal, which exhibits essentially unity gain, optimizes reception.
FIG. 1 is a block diagram of a typical indoor television antenna having a switchable amplifier circuit, more generally referred to as a television signal switching circuit 10. The switching circuit 10 includes an amplification/unity gain signal path 12 and a game port signal path 14. The amplification/unity gain signal path 12 is coupled in series between an antenna 16 and a television receiver 18.
The amplification/unity gain signal path 12 includes the series connection of an amplifier circuit 20, a direct current (DC) blocking capacitor 21, and a diode isolation circuit 23. The antenna 16 is coupled to an input of the amplifier circuit 20, and an output of the amplifier circuit 20 is coupled to a first end of the capacitor 21. A second end of the capacitor 21 is coupled to an input of the diode isolation circuit 23, and the output of the diode isolation circuit 23 is coupled to the television receiver 18. The amplifier circuit 20 is also coupled to an amplification control circuit 22, which can selectively, under the control of a user, supply power to the amplifier circuit 20 and adjust the amount of gain provided by the amplifier circuit 20.
The diode isolation circuit 23 includes two diodes coupled in series. The anode of a first diode is coupled to the input of the diode isolation circuit 23, and selectively coupled to a DC bias. The cathode of the first diode is coupled to the anode of a second diode, and the cathode of the second diode is coupled to the output of the diode isolation circuit 23.
The game port signal path 14 is coupled in series between a game port input 17 and the television receiver 18. The game port signal path 14 includes the series connection of a DC blocking capacitor 25 and a diode isolation circuit 27. The game port input 17 is coupled to a first end of the capacitor 25, and a second end of the capacitor 25 is coupled to an input of the diode isolation circuit 27.
The diode isolation circuit 27 is substantially the same as the diode isolation circuit 23 already described. The output of both diode isolation circuits 23, 27 are coupled to each other, a first end of a direct current (DC) leakage resistor 29, and the television receiver 18. A second end of the resistor 29 is coupled to ground and provides a path for residual charge introduced by the DC bias to escape.
If the DC bias is applied to the diode isolation circuit 27 in the game port signal path 14, the diodes in the isolation circuit 27 become forward biased and a game port signal in the game port signal path 14 is allowed to pass to the television receiver 18. By applying the DC bias to the isolation circuit 27 in the game port signal path 14, the DC bias is not applied to the isolation circuit 23 in the amplification/unity gain signal path 12. This causes the diodes in the path 12 to remain off or in a non-conductive state, which isolates the output of the amplifier circuit 20 from the television receiver 18.
Likewise, if the DC bias is applied to the diode isolation circuit 23 in the amplification/unity gain signal path 12, the diodes in the isolation circuit 23 become forward biased and a television signal in the amplification/unity gain signal path is allowed to pass to the television receiver 18. By applying the DC bias to the isolation circuit 23 in the amplification/unity gain signal path 14, the DC bias is not applied to the isolation circuit 27 in the game port signal path 14. This causes the diodes in the path 14 to remain off or in a non-conductive state, which isolates the game port input 17 from the television receiver 18.
If the user chooses to provide power to the amplifier circuit 20 via the amplification control circuit 22, the television signal seen by the television receiver 18 exhibits that amount of gain chosen by the user. In contrast, if the user chooses not to provide power to the amplifier circuit 20, the amplifier circuit 20 essentially becomes a short circuit and the television receiver 18 sees the television signal with essentially unity gain.
However, one disadvantage with the conventional approach shown in FIG. 1 is that the diode isolation circuits 23, 27 do not completely isolate the amplification/unity gain signal path 12 and game port signal path 14. For instance, portions of the amplification/unity gain signal path 12 remain in the circuit even if the game port signal path 14 is chosen. These portions act as stubs terminated by an impedance that creates reflections, and thus noise, in the television signal. In addition, the diodes in the isolation circuit 23 introduce leakage of either the television signal or the game port signal into the chosen path due to their poor isolation.
Thus, the approach shown in FIG. 1 does not result in two independent and isolated paths. Rather, this approach results in two essentially composite paths, each of which includes signal reflections and leakage introduced by the path not selected.
It is an object of the present invention to provide an apparatus for improving the reception of a television signal by a television receiver.
It is a further object of the present invention to provide an apparatus for reducing signal reflection, crosstalk, and noise in and between alternate paths of a broadcast, cable or game port television signal having different gains associated therewith.
It is yet a further object of the present invention to provide an apparatus for amplifying off air broadcast television signals over a broad range of gains, which increases the associated signal-to-noise ratio (SNR) without disrupting cable or game port signals.
It is still another object of the present invention to provide an apparatus for selectively applying unit gain or a variable gain to off air broadcast television signals, which increases the SNR of the television signal without disrupting cable or game port signals.
It is a further object of the present invention to provide an apparatus for maximizing isolation between alternate paths of a broadcast, cable or game port television signal having different gains associated therewith.
In accordance with one form of the present invention, a television signal switching circuit is provided, which includes an amplification signal path and a unity gain signal path. A first switching circuit and a second switching circuit, which preferably include relays, substantially isolate the amplification signal path from the unity gain signal path. One or more antennas receive the television signal and output it to an input of the first switching circuit. The amplification and unity gain signal paths are coupled in parallel between the first and second switching circuits. An output of the second switching circuit is coupled to a third switching circuit which isolates the output of the second switching circuit from a game port input. The third switching circuit selectively routes either the output of the second switching circuit or the game port input to the television receiver.
A switching control circuit outputs a switching control signal, which controls the first, second, and third switching circuits. In response to the switching control circuit, the first and second switching circuits route the received television signal through either the amplification signal path or the unity gain signal path, and the third switching circuit routes either the output of the second switching circuit or the game port input to the television receiver. Thus, since the amplification, unity gain, and game port signal paths are isolated and the television signal does not flow through any portion of the path not selected, signal reflections, noise, and crosstalk between these paths are minimized. The switching control circuit also provides a gain control signal to the amplifier, which can adjust the gain applied to the television signal in the amplification signal path.
In accordance with yet another form of the present invention, the first and second switching circuits are omitted and the antenna is coupled to the third switching circuit via the amplification signal path.
In accordance with still another form of the present invention, an isolation circuit is substituted for the first switching circuit.
In accordance with yet another form of the present invention, a power combiner circuit is substituted for the second switching circuit.
In accordance with still another form of the present invention, a power divider circuit is substituted for the first switching circuit.